Basic Definition of Terms

Air Conditioning

The process of treating air so as to control simultaneously its temperature, humidity, cleanliness and distribution to meet the requirements of the conditioned space

Ventilation

Process of supplying or removing air by natural or mechanical means to or from any space. Such air may or may not have been conditioned.

Psychrometry

study of the properties of mixtures of air and water vapor

Psychrometer

an instrument used in the study of the properties of air

Saturated Air

Air whose condition is such that any decrease in temperature will result in condensation of the water vapor into liquid.

Unsaturated Air

Air containing superheated vapor.

Moist Air

A binary mixture of dry air and water vapor

Dry Air

Non condensing components of the mixture, mainly the nitrogen and the oxygen.

Vapor

Condensable component of the mixture the water vapor which may exist in a saturated or superheated state.

Properties of Air

Temperature
Pressure
Humidity Ratio
Relative Humidity
Specific Volume
Density

Enthalpy

Degree of Saturation

Dry bulb temperature

temperature of air as it registered by an ordinary thermometer

Wet bulb temperature

temperature of air as registered by a thermometer whose bulb is covered by a wetted wick and exposed to a current of rapidly moving air.

Wet bulb depression

difference between the readings of the wet and dry bulb thermometers

Dewpoint Temperature

Saturation temperature corresponding to the actual pressure of the steam in air or the temperature at which condensation of moisture begins when the air is cooled at constant pressure.

Pressure

Total pressure of air-water vapor mixture is the sum of partial pressure of dry air and water vapor.

Humidity Ratio

Ratio of the mass of water vapor to the mass of dry air. It is also known as moisture content, mixing ratio or specific humidity.

Relative Humidity

Ratio of the partial pressure of water vapor in the air to the saturation pressure corresponding to the temperature of the air.

Specific Volume

Number of cubic meters of mixture per kilogram of dry air.

Density

Reciprocal of specific volume

Degree of Saturation

Ratio of air humidity ratio to the humidity ratio of saturated air at the same temperature

Psychometric Chart

Graphical Representation of thermodynamic properties of moist air.

Air Mixing

A chamber in which the recirculating air is mixed with the air from outdoors.

Air conditioner

a mechanism primarily for comfort cooling that lowers the temperature and reduces the humidity of air in buildings.

Cooling Tower

Device commonly used to cool condenser water in power and refrigerating plants.

Range

Reduction in temperature of water through the cooling tower

Approach

Difference between the wet-bulb temperature of the entering air and temperature of the leaving cool water.

Cooling Tower Efficiency

Cooling effectiveness of a cooling tower

Heat balance

Heat absorbed by air = Heat rejected by water

Dryer

Removal of relatively small amounts of water or other liquid from the solid materials

Types of Dryers

Continuous Dryer
Ratch Dryer

Classification of Dryers

Rotary Dryer
Tower Dryer
Hearth Dryer
Centrifugal Dryer
Tray Dryer
Infrared Ray Dryer

Rotary Dryer

Most commonly used dryer which consist of a rotating cylinder inside which the materials flow while getting in contact with hot gases.

Tower Dryer

Consist of a vertical shaft in which the wet feed is introduced at the top and falls downward over baffles while coming in contact with the hot air which rises and exhaust at the top.

Hearth Dryer

A type of dryer in which the material to be dried is supported on a floor through which the hot gasses pass.

Centrifugal Dryer

Consist of centrifuge revolving at high speeds causing the separation, by centrifugal force of the water from the material.

Tray Dryer

Consist of trays, carrying the materials to be dried, placed in a compartment or moving conveyor.

Infrared Ray Dryer

Consist of infrared lamps in which the rays are directed to the articles to be dried.

Hygroscopic Material

Hygroscopic

Hygroscopic

substances which are particularly variable in the moisture content which they can possessed at different times.

Bone Dry Weight

Dry weight is the final constant weight reached by a hygroscopic substance after being dried out.

Regain

Hygroscopic moisture content of a substance expressed as a percentage of the bone dry weight of the material

Moisture Content

Expressed as a percentage of the gross weight of the body and may refer to both hygroscopic and purely surface moisture.